Catalyzed metal fuel



3,006,745 CATALYZED METAL FUEL Harry A. Toulmin, Jr., Dayton, Ohio,assignor to The Commonwealth Engineering Company of Ohio, Dayton, OhioNo Drawing. Original application Sept. 2, 1954, Ser. No. 453,933, nowPatent No. 2,890,108, dated June 9, 1959. Divided and this applicationSept. 29, 1958, Ser. No.

5 Claims. (Cl. 52-.5)

This invention relates to improved fuels and methods of increasing thecalorific value of fuels and is a division of application Serial No.453,933 filed September 2, 1954, now Patent No. 2,890,108.

The invention is particularly useful in providing a fuel comprising forexample powdered metals which burn easily and quickly to produce ultrahigh heating temperatures and high velocity gases and such as heretoforehas not been attained with conventional fuels.

It is a principal object ofetheeinvemionftmsret'idea2-4natedomenadmixethlheflakesnofsmetalkeg, ah1@ catalyzed powderedmetal useful as a suitable fuel in jet airplane engines, gas turbines,explosives, propellants, rockets, power plants, and the like, as used inthe fields of aviation, rail transportation, agricultural distributionsys- 1 an i 3,006,745 Patented Oct. 31, 1961 min mixed with a catalystsuch as a metallic soap. The particle size of the metal is generally onthe order of microns or less and preferably a micron or less indiameter. This mixture of metal dust and metallic material maybe used asa dry powder fuel or admixed with liquid hydrocarbon to form a slurry.

To catalyze and enhance the combustion rate of the powdered metalmaterials and produce a high temperatems for fertilizer andinsecticides, destruction of vegetation, and as may be useful formilitary purposes, as for example flame throwers, fire bombs, etc.

It is another object of the invention to provide a composition useful asfuels, explosive products or as ignition catalysts for initiating andpromoting high temperature reactions and'high' veleeity hat gasese H iIt is another object of the invention to provide a com bustiblecomposition which has very short flame propulsion area and whichexhibits an accelerated rate of combustion due to the highly pyrophoriccharacter of the fuel mixture.

It is another object of the invention to provide a powdered metal fuelmixture which may be used in the form of a slurry containing metal andauto-oxidation catalyst dispersed in a liquid hydrocarbon and whichproduces a large amount of exothermic heat during combustion.

A still further object of the invention is to provide a method foraccelerating the combustion of powdered metal and the like materialswhereby the flame spreads through the mass of fuel and brings about theexploding and rapid disintegration of each of the particles of themetal. The powdered fuel mixture of the invention is characterized byexhibiting a high flame speed during combustion and the production of ahigh pressure area. By utilizing a proper concentration of the metalpowder or metal dust, and auto oxidation catalysts, and dispersing thesame while introducing a suflicient supply of air or oxygen to providefor complete combustion of the metal dust, maximum evolution of heat isobtained during combustion of the dust.

In accordance with the invention, a basic process is provided forobtaining the maximum heat of combustion from fuels, especially powderedmetals. The invention will be described more particularly with referenceto the use of powdered aluminum and magnesium metals, however, othercombustible materials of similar nature also may be used or admixedtherewith to provide an improved fuel.

In preparing the fuel mixture powdered metal material for examplealuminum or magnesium metal particles are 5 like. This slurry of oil andmetal particles may be easb aamer suchasgasolinegter a:

ture reaction, there is introduced a small amount of a metallic soap ormixture of such metallic soaps, for example 0.1 to 5.0% by weight of thepowdered metal constituents comprises a metallic soap such as astearate, palmitate, oleate, ricinoleate, etc., of aluminum, magnesium,titanium, zirconium, tin and the like which compounds exhibit autooxidation catalytic properties. These metals are referred to hereinafterand in the claims as light metals.

The metal particles of the fuel mixture are in the form of dust orflakes, with metallic soap being preferably num metal flakes coated withaluminum stearate forms an excellent fuel mixture. Mercury metal insmall amounts, e.g., 0.1 to 1.0% by weight of the fuel powder mixturealso may be added to enhance the catalytic action. Mercury compounds,such as mercury peroxide or fulminate, may be used in place of mercurymetal for this purpose.

Where the fuel is to be employed as a liquid, the metal particles in theform of flakes or dust and catalytic substance are dispersed in a liquidhydrocarbon, for example kerosene, gasoline, diesel oil, etc., whichprovides a liquid cembastiblemarriea far the spcwderedmmme ial mfii Sucha fuel is useful for operating jet engines and high temperature fueloperated prime movers, and where the maximum B.t.u.s are to be extractedfrom the burning fuel in a predetermined time.

For promoting the oxidation and increasing the speed of burning of thefuel, a peroxide such as hydrogen or benzyl peroxide etc. may beintroduced into the fuel mixture initially or during the burning of thesame. For this purpose 0.5 to 2.0% by weight of the fuel solids maycomprise a peroxide.

As specific examples of the improved powdered metal fuel of thisinvention aluminum metal dust, preferably as powdered metal foil of aparticle fineness of an average size of one micron is coated withaluminum stearate (0.1 to 5.0% by weight of the powdered metal mixture).In place of aluminum metal, magnesium metal titanium or other readilyoxidizable metals such as zinc, tin and zirconium, titanium, etc. metalparticles in the form of dust or flakes, may be used. Aluminum flakescoated with a small amount of aluminum or magnesium stearate or the likemetallic soap as aforementioned provides a suitable fuel mixture.

The metallic soap utilized as auto oxidation catalysts are preferablysalts of metals in groups II, III and IV of the periodic table,representatives of which are the stearates or palmitates of aluminum,magnesium, titanium, zirconium and tin.

The powdered metal fuel mixture also may be used in the form of aslurry, the same being admixed with liquid hydrocarbon. For example,powdered metal such as aluminum metal flakes, with or without metallicsoap, e.g., aluminum stearate is introduced into a liquid hydronil,112L161 m m sprayed into a combustion chamber of engine and mixed withair or oxygen and burned. In general, one to twenty-five parts of thesolid fuel constituents to 100 parts by weightof the liquid hydrocarbonprovides a suitable liquid fuel mixture. Higher or lower proportionateamounts of the liquid hydrocarbon and powdered fuel constituents may beemployed as needed, to provide a fuel having the requisite consistencyand burning characteristics desired. The powdered metal may be mixedwith the liquid hydrocarbon either before or during burning of the fuel.Additional oxygen in the form of peroxides, e.g., benzyl peroxide may beadded as a supplement to air for increasing the speed of burning orcombustion of the fuel mixture as aforementioned.

The presence of the auto oxidation catalyst in sufiicient amount tocatalyze the reaction is an esential constituent of the powdered metalfuel. The metal particles which are combustible and tend to vaporizereadily produce a high temperature reaction during the combustion. Thevery high temperatures produced during the catalyzed reaction causes themetal particles to be rapidly disintegrated and vaporized. Thecombustion of the metal powder thus proceeds at a high rate, the hightemperature and explosive action being enhanced by the catalytic actionof the metallic soap. The high temperatures produced combined with theviolent disintegration and vaporization of the powdered metal particlesis believed to account for the unexpected high calorific valuesproduced.

Heretofore, in the combustion of metal particles, the maximum B.t.u.shave not been obtained principally because the initial heating of theparticles did not result in the production of temperatures high enoughto disintegrate and vaporize the metal and permit air or oxygen to comein contact with all the powdered metal particles and support itscombustion to completion. In other words, under conventional combustionreactions using powdered metals there was always a certain minimumamount of the particles which were not burned to completion but passedoff as smoke.

In accomplishing the high combustion and maximum extraction of B.t.u.sfrom powdered metal material in accordance with this invention, it isrequisite that the reaction be conductedsothat the boiling point orvaporization point of the combustion material be lower than the flametemperature and that the heat or vaporization is lower than the energyrequired to initiate rapid surface oxidation or combustion.

The catalytic action of metallic soaps facilitates the burning of themetal dust and provides a high temperature reaction so that the maximumB.t.u.s are obtained from the metal dust particles. During combustion ofthe fuel the high temperatures produced rapidly transform the metalparticles into gases at high temperature.

Further, metal powders such as aluminum or magnesium dust when used witha petroleum hydrocarbon carrier such as gasoline, kerosene, diesel oilor the like provides a fuel which is more sensitive to ignition andproduces a powdered metal fluid mixture wherein the flame produced bycombustion proceeds more rapidly through the fuel, than when the dustparticles are employed alone. Moreover, the combustible gases formed bythe hydrocarbon likewise enhance this combustion. The efl'iciency of thecombustion and high extraction of B.t.u.s is further facilitated due tothe catalytic action of the metal particles such as magnesium oraluminum powder, particularly in the presence of hydrogen which isformed by decomposition of moisture present and under the hightemperature reaction conditions during combustion of the fuel.

In addition to the high rate of reaction and production of hightemperatures during combustion of these metal dust particles and whichcomprise oxygen adsorbed on the dust particles, it has been found thatthe addition of a small amount of a metallic soap such asaforementioned,

for example aluminum, magnesium stearate or oleate or the like, willfurther accelerate this ignition and flame propagation during combustionof the fuel. This is probably due to the fact that the porous surface ofthe particles adsorb gas from the surrounding atmosphere and themetallic soap catalyzes the reaction.

To control the combustion and prevent explosion and to facilitatecombustion an excess of oxygen in the atmosphere is preferred and isintroduced into the fuel either from the air or from the use of amixture of air and peroxide, as heretofore explained. In this manner itis possible to produce the combustion at a lower ignition temperatureand increase the rate of combustion and the adsorption of oxygen on thedust particles.

Metal particles such as aluminum, magnesium, zinc and the likeoxidizable material in the form of dust ignited in the presence ofmetallic soap catalytic agent burns at a high rate and temperature. Thecombustion rate promoting catalysts produce a powdered metal fuel whichhas a lower explosive limit or temperature, particularly in the presenceof methane, oxygen or air, and results in the enhancement of thecombustion of the fuel.

Control of the combustion and explosive properties of the powdered metalcan be effected by utilizing different oxidizing agents and in variousproportions. In this manner the incendiary action of the fuel may becontrolled so as to either accelerate the combustion or burning up ofthe fuel particles or slow down their combustion as may be required inthe use of the fuel. Thus, for making a fuel useful in internalcombustion engines utilizing powdered metal material, the combustion maybe speeded up by the use of metallic soap and peroxide catalysts so thatthe mixture will burn and provide the high temperature reaction gasesnecessary to propel the piston in a predetermined time. In otherinstances where the fuel is required to burn more slowly, the use ofnegative catalysts such as those which do not accelerate the combustionbut tend to decelerate the combustion are incorporated in the fuel.

In the case of metal dust such as aluminum dust and similar metal dust,the ignition of the same is believed to have an electric or electronicorigin as opposed to thermal ignition. The electrical discharges orionization is believed to produce ozone and aluminum oxide (A1 0 whichreacts with the fine dust particles and initiates the decomposition ofthe same and flame propagation during the combustion of the fuel.

The electrical ignition depends largely upon the production of asufficient concentration of charged particles and which results fromelectronic collisions due to ionization of the materials or the presenceof ions or ionized particles in the explosive mixture. This electronicphase of the combustion is believed to play an important roll in theincreased efficiency of the fuel of this invention. The same issubstantially true in the case of thermal ignition.

-It is also considered to be immaterial whether the theory ofpredistillation of dust during ignition and combustion takes place orwhether such a theory may be used to explain what happens to the fuelduring combustion, or whether it involves some other theory for theproduction of the improved results. In the case of the predistillationtheory of dust ignition, it is believed that all dust ignition involvespurely a gas or vapor explosion and that the energy of the ignitionsource provides heat to decompose the dust particles thus causing theevolution of the volatile matter. In this manner the volatilized gassyparticles mix more readily with air and ignite and the combustionproceeds at a high rate and the heat produced in turn further heats andvolatilizes other particles not yet volatilized.

One of the objections made to the above theory has been that theignition temperature of some dust, including coal, are lower than theignition temperatures of the gases involved such as methane or the likehydrocarbon.

quently the temperature above the ignition point of the solid causing itto distill and eventually to ignite, thus initiating the combustionreaction.

In the preferred process of carrying out the combustion of the novelfuel of this invention, it is sought to have the concentration such aswill prot idesaicniemaheat le to produce complete oxidation of the dustparticles and thus release the maximum B.t.u.s. The heat produced bycomplete oxidization of a portion of the dust particles in the availableoxygen is enough to heat the rest of the dust in the mixture to bringthe same to the ignition temperature. Theoretically, neglectingdisassociation, the strongest explosion or greatest explosive forceshould be produced at a concentration corresponding to stoichiometricweight mixtures of the fuel ingredients. This can 6 source, the timingof ignition and the interpretation of what constitutes limitingflamepropagation.

The igniting energy of these dust clouds vary with the fineness, themoisture content and somewhat with the concentration in the cloud. Forinstance, undispersed layers of zirconium powder have been ignited bysparks of less than 1 microjou'le energy while other dusts takeconsiderably stronger sparks. The igniting energy of dust clouds in airranges from about 10 millijoules to several imllm The igniting sourcegenerally preferred is a high voltage induction' spark. When these dustsare thus ignited the pressure is developed to more than 150 lb./in. andrises to an average rate of pressure of about 5000 lb./in. per secondand the maximum rates to more than 10,000 lb./in. per second. When usinga high voltage continuous induction spark and dispersing the dustthrough a furnace at 850 C. a satisfactory result can be secured.

The minimum concentration of coal dust that will be computed if thechemical composition of the dust is propagate large scale explosions isapproximately known and provided complete combustion of themateriai esgiiter{ee%ce#ft} cf Pressm e is aemly le t is assumed to take place. Inpractice, however, somewhat richer dust mixtures are found to be themost explosive.

The adjustment of these mixtures to provide the great- 5 est heatproduction is facilitated by the catalytic action of the metal powder,for example powdered metal such as aluminum, magnesium, zinc, tin, etc.,and the fluid carrier which is preferably hydroearben akdesefi" lb./in.and flame velocities in excess of 6000 ft./sec. have been accomplishedby the employment of the thermal properties of the metal dust and thecatalysts, e.g., aluminum flakes and similar other dusts. As herebeforestated, in the presence of a liquid hydrocarbon fuel and oxygen, it ispossible to achieve temperature and gas velocities of great magnitudeand by adjusting the fineness the rnaterialsan elved the%cunt efmeista-repraeat 7 The initial temperature, pressure, oxygen content, hu-8 and the oxygen, the maximum energy can be released.

midity, specific heat and heat conductivity of the atmosphere all arefactors which influence the dust explosion. The presence of oxygen is,of course, a most important factor.

It will thus be seen that the present invention provides a novel fueland method of producing high temperature combustion reactions, andwherein metal dust particles form a principal constituent.

As a source of ignition it is preferred to utilizeafiame 35 Further, theinvention provides a fuel wherein a or hot surface. The presence ofmoisture which normally is a constituent of the mixture is advantageoussince it reacts with the metal powder and similar materials at thereaction temperatures and results in the evolution of catalyzed metaldust is utilized to produce a high temperature fuel and wherein themaximum B.t.u. values are obtained.

It is understood that various changes and additions hydrogen gas. Theproduction of hydrogen gas is efmay be made in compounding the fuel ofthis invention fected particularly at elevated temperatures whereindecomposition and ionization of moisture is produced. This reduces thesurface oxide coating which would otherwise tend to form onto theparticles and thus makes the fuel mixture highly sensitive to ignitionand combustion.

Other pyrophoric metal dust particles may be present such as finelydivided metal powders of iron, manganeses, copper, uranium, nickel,zirconium and others, metal oxides, hydrides carbidesrnitridm' anrt nalso oxidize so rapidly on exposure to air that t and ignite. Whilethere is no apparent agreement regarding the exact mechanism of thepyrophoric ignition, it is believed that the process varies somewhatwith the type of dust, its fineness and surface character. 7

The basic discovery in this invention is that by utilizing a combinationof combustible metal powder dust with powdered coal dust that thecombustion can be achieved and controlled whereby the maximum liberationof gas and heat results from the reaction. The pyrophricity of thesedusts, as hereinbefore mentioned, is believed to be" related to ametastable internal equilibrium in the powders. Thus, one of theadvantages of utilizing these metal dusts of pyrophoric character, suchas aluminum and/or magnesium metal powder or dusts, is that with asuflicient dispersion of these extremely fine particles, the same willself-ignite by an electrostatic spark discharge within the cloud ofdust.

Particularly satisfactory resuits have beensecured 5 the spirit andscope of this invention, and which are more particularly set forth inthe appended claims.

What is claimed is: 1. A fuel consisting essentially of a solid fuelcom- 7. L m ef tieely s'ided metal seleeted rormthe g'eupe hey h 50consisting of aluminum, magnesium, titanium, zinc,

tm and zirconium, together with mercury metal in an amount of 0.10 to1.0% by weight of the fuel mixture, and aluminum stearate in the amountof 0.1 to 5.0% by weight of the finely divided metal.

2. A fuel consisting essentially of a solid fuel composed of finelydivided metal, and a metallic soap, said finely divided metal beingselected from the group conducting of aluminum, magnesium, titanium,zinc, tin and zirconium, together with mercury metal in an amount of0.10 to 1.0% by weight of the fuel mixture, and said metallic soap beingselected from the group consisting of the stearates, palmitates,ricinoleates and oleates of the metals selected from the groupconsisting of aluminum, magnesium, titanium, zirconium and tin, saidmetallic 55 soap being introduced in the amount of 0.1 to 5.0% by weightof the finely divided metal.

3. A fuel consisting essentially of a solid fuel composed of finelydivided aluminum metal, together with mercury metal in an amount of0.10t6 1.0% by wfight dust Samples of fine! than 200 mesh- This M can beof the fuel mixture, and aluminum stearate, said finely passed throughan electrically heated cylindrical alundumcore furnace construction forignition. The ignition temperatures for the dust will range from about200 C. to more than 1000 C. These figures depend upon thedispersibility, fineness, uniformity of the dust, the ignition dividedaluminum metal having a particle size of an averaged 1 micron and thealuminum stearate consisting of 0.1 to 5.0% by weight of the finelydivided aluminum metal.

4. A fuel consisting essentially of a solid fuel composed of finelydivided magnesium metal, together with fuel mixture, and aluminumstearate, said finely divided mercury metal in an amount of 0.10 to 1.0%by weight aluminum metal having a particle size of an average of of thefuel mixture, and aluminum stearate, said finely 1 micron, said aluminumstearate consisting of 0-1 t divided magnesium metal having a particlesize of an 5.0% by weight of the finely divided aluminum metal. averageof 1 micron, said' aluminum stearate consisting 5 of 0.1 to 5.0% byweight of the finely divided magnesium References cued m'the file ofPawnt metal. Anderton: Aviation Week, Nov. 12, 1956, pp. 51, 3,

5. A fuel consisting essentially of a solid fuel composed 5, 7, offinely divided aluminum metal, together with mercury Grant: The Journalof Space Flight, vol. 2, No. 10,

metal in an amount of 0.10 to 1.0% by weight of the 10 December 1950,pp. 3-5.

1. A FUEL CONSISTING ESSENTIALLY OF A SOLID FUEL COMPOSED OF FINELYDIVIDED METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, MAGNESIUM,TITANIUM, ZINC, TIN AND ZIRCONIUM, TOGETHER WITH MERCURY METAL IN ANAMOUNT OF 0.10 TO 1.0% BY WEIGHT OF THE FUEL MIXTURE, AND ALUMINUMSTEARATE IN THE AMOUNT OF 0.1 TO 5.0% BY WEIGHT OF THE FINELY DIVIDEDMETAL.